<s>
Quantitative	B-Algorithm
Susceptibility	I-Algorithm
Mapping	I-Algorithm
(	O
QSM	O
)	O
provides	O
a	O
novel	O
contrast	O
mechanism	O
in	O
Magnetic	B-Algorithm
Resonance	I-Algorithm
Imaging	I-Algorithm
(	O
MRI	B-Algorithm
)	O
different	O
from	O
traditional	O
Susceptibility	B-Algorithm
Weighted	I-Algorithm
Imaging	I-Algorithm
.	O
</s>
<s>
The	O
voxel	O
intensity	O
in	O
QSM	O
is	O
linearly	O
proportional	O
to	O
the	O
underlying	O
tissue	O
apparent	O
magnetic	O
susceptibility	O
,	O
which	O
is	O
useful	O
for	O
chemical	O
identification	O
and	O
quantification	O
of	O
specific	O
biomarkers	O
including	O
iron	O
,	O
calcium	O
,	O
gadolinium	B-Algorithm
,	O
and	O
super	O
paramagnetic	O
iron	O
oxide	O
(	O
SPIO	B-Algorithm
)	O
nano-particles	O
.	O
</s>
<s>
Due	O
to	O
its	O
quantitative	O
nature	O
and	O
sensitivity	O
to	O
certain	O
kinds	O
of	O
material	O
,	O
potential	O
QSM	O
applications	O
include	O
standardized	O
quantitative	O
stratification	O
of	O
cerebral	O
microbleeds	O
and	O
neurodegenerative	O
disease	O
,	O
accurate	O
gadolinium	B-Algorithm
quantification	O
in	O
contrast	O
enhanced	O
MRI	B-Algorithm
,	O
and	O
direct	O
monitoring	O
of	O
targeted	O
theranostic	O
drug	O
biodistribution	O
in	O
nanomedicine	O
.	O
</s>
<s>
In	O
MRI	B-Algorithm
,	O
the	O
local	O
field	O
induced	O
by	O
non-ferromagnetic	O
biomaterial	O
susceptibility	O
along	O
the	O
main	O
polarization	O
B0	O
field	O
is	O
the	O
convolution	B-Language
of	O
the	O
volume	O
susceptibility	O
distribution	O
with	O
the	O
dipole	O
kernel	O
:	O
.	O
</s>
<s>
This	O
spatial	O
convolution	B-Language
can	O
be	O
expressed	O
as	O
a	O
point-wise	O
multiplication	O
in	O
Fourier	B-Algorithm
domain	I-Algorithm
:	O
.	O
</s>
<s>
This	O
Fourier	B-Algorithm
expression	O
provides	O
an	O
efficient	O
way	O
to	O
predict	O
the	O
field	O
perturbation	O
when	O
the	O
susceptibility	O
distribution	O
is	O
known	O
.	O
</s>
<s>
However	O
,	O
the	O
field	O
to	O
source	O
inverse	O
problem	O
involves	O
division	O
by	O
zero	O
at	O
a	O
pair	O
of	O
cone	O
surfaces	O
at	O
the	O
magic	O
angle	O
with	O
respect	O
to	O
B0	O
in	O
the	O
Fourier	B-Algorithm
domain	I-Algorithm
.	O
</s>
<s>
In	O
human	O
brain	O
quantitative	B-Algorithm
susceptibility	I-Algorithm
mapping	I-Algorithm
,	O
only	O
the	O
local	O
susceptibility	O
sources	O
inside	O
the	O
brain	O
are	O
of	O
interest	O
.	O
</s>
<s>
COSMOS	O
utilizes	O
the	O
fact	O
that	O
the	O
zero	O
cone	O
surface	O
in	O
the	O
Fourier	B-Algorithm
domain	I-Algorithm
is	O
fixed	O
at	O
the	O
magic	O
angle	O
with	O
respect	O
to	O
the	O
B0	O
field	O
.	O
</s>
<s>
Quantitative	O
susceptibility	O
maps	O
obtained	O
from	O
in	O
vivo	O
human	O
brain	B-Algorithm
imaging	I-Algorithm
also	O
showed	O
high	O
degree	O
of	O
agreement	O
with	O
previous	O
knowledge	O
about	O
brain	O
anatomy	O
.	O
</s>
<s>
A	O
unique	O
advantage	O
of	O
MRI	B-Algorithm
is	O
that	O
it	O
provides	O
not	O
only	O
the	O
phase	O
image	O
but	O
also	O
the	O
magnitude	O
image	O
.	O
</s>
<s>
The	O
underdetermined	O
data	O
in	O
Fourier	B-Algorithm
domain	I-Algorithm
is	O
only	O
at	O
the	O
location	O
of	O
the	O
cone	O
and	O
its	O
immediate	O
vicinity	O
.	O
</s>
<s>
For	O
this	O
region	O
in	O
k-space	B-Algorithm
,	O
spatial-frequencies	O
of	O
the	O
dipole	O
kernel	O
are	O
set	O
to	O
a	O
predetermined	O
non-zero	O
value	O
for	O
the	O
division	O
.	O
</s>
<s>
Investigation	O
of	O
more	O
advanced	O
strategies	O
for	O
recovering	O
data	O
in	O
this	O
k-space	B-Algorithm
region	O
is	O
also	O
a	O
topic	O
of	O
ongoing	O
research	O
.	O
</s>
<s>
Thresholded	O
k-space	B-Algorithm
division	O
only	O
requires	O
a	O
single	O
angle	O
acquisition	O
,	O
and	O
benefits	O
from	O
the	O
ease	O
of	O
implementation	O
as	O
well	O
as	O
the	O
fast	O
calculation	O
speed	O
.	O
</s>
<s>
This	O
provides	O
a	O
new	O
way	O
for	O
in	O
vivo	O
quantification	O
of	O
gadolinium	B-Algorithm
or	O
SPIO	B-Algorithm
concentrations	O
.	O
</s>
